Spectrally resolved third-order nonlinearities in polydiacetylene microcrystals: influence of particle size

The on- and near-resonant third-order nonlinear optical response of polydia cetylene microcrystals in suspension was studied by the Z-scan technique wi th tunable picosecond pulses. The absorptive and refractive contributions t o the excitonic-dominated nonlinearity were fully resolved at several wavel engths. Microcrystals of two different average sizes were studied, and a co mparison of their nonlinear coefficients; was made. A three-level model for the nonlinear response is presented that shows good agreement with the exp erimental data. (C) 1998 Optical Society of America [50740-3224(98)00812-1] OCIS codes: 190.4400, 160.4890, 300.6400.